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The principle of most modern day clean rooms is based upon laminar flow, or to be more precise unidirectional airflow. Parallel streams of air, moving at a uniform velocity of 0.3 to 0.45 metres per second are blown across the room with as little turbulence as possible. The principle is based on expelling any dust in the airflow by the shortest route. In general, the greater the frequency with which the air is renewed, the lower the contamination build up in the room and the greater the rate at which the impurities are diluted

The most common types of clean room found today are either vertical down flow or horizontal cross flow. In a vertical down flow clean room, air enters the room via filters in the roof and exits through vents in the floor. Although this design has proven to be technically efficient and can attain the highest of specifications, it is extremely costly in both capital and maintenance.

In a horizontal cross flow clean room, filtered air enters the room from   one side wall and is exhausted above the floor in the sidewall opposite and/or re-circulated via a bank of filters. The air velocity has to be established at a sufficiently high level to ensure that dust particles do not thermally migrate from the laminar flow.

The design of a clean room has to accommodate many factors including:

Process - what is the client intending to use the room for?

Longevity - how long is the room expected to last?

Traffic  - how many times will personnel enter / leave the room per hour/ day?

Heat loading - what heat is equipment / personnel outputing to the room?

Air extraction  - how much air is being extracted for processes?

Air conditioning - is comfort cooling / heating required or something more stringent? What ambient max and min temperature parameters are to be specified?

Humidity -  does this need to be controlled and if so within what parameters?